Aero Tech Fuel Tanks | Aero Tech Services -- the standard in fuel cells

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by Schultzeworks

from DIRTsports Magazine

When it came time to outfit our Project Elf Class 11 racer with a fuel cell, we had a variety of off-the-shelf options. While all safe and durable, we ultimately decided on making a custom cell for our little Bug for a variety of reasons. Prevalent among these is that an enclosure built specifically to fit the tight confines of the Elf would allow us to maximize the lack of space on the inside of the VW. With the fuel cell taking up the space behind the occupants, a custom shape would give us additional nooks and crannies to stuff valuable spares. It would also give the students at the Fab School a chance to hone their aluminum skills. What's more, building our own shape yielded the benefit of cramming as much fuel in the Elf as we dared.

While the students would handle the construction of the outer skin, we turned to Aero Tech to build the all-important internal fuel bladder. While it sounds simple, a fuel bladder can be quite complicated, adorned by multiple sumps, fuel traps and fuel pickup points. For example, a NASCAR vehicle making only left-hand turns may only need a pickup in the outboard corner for reliable fuel delivery. In contrast, a road-race vehicle that makes repeated left and right hi-G turns, in addition to its high-rate braking and acceleration, will require fuel pickups

in multiple locations. Off-road race rigs fall between these two extremes.

AeroTech builds fuel bladders that are unique in the industry. All Aero Tech fuel bladders are two-ply nit rile rubber, covered by a fuel-barrier adhesive and then covered in an outer layer of nylon-reinforced rubber. This type of construction lasts longer than single-ply construction and has been the military standard since the 1940s. For race cars and trucks, the fuel barrier material is .030-inch thick and two layers are applied. Then, an overlay is done in a fuel-barrier adhesive along with a layer of .045-inch rubber-coated nylon for protection. The result can be as much as .250-inch thick at the corners and seams.

Aero Tech Services can manufacture new fuel bladders for an existing fuel cell or build a custom fuel bladder. The company has the ability to work from a blueprint, or customers can ship a fuel cell and have the bladder constructed to match. Aero Tech does not manufacture the outer sheet-metal shells but can refer customers to a reliable local shop for this part of the service. In addition, Aero Tech offers custom fittings if off-the-shelf items are not suitable. Follow along as we illustrate what it takes to build a world-class fuel bladder.

Typically, automotive fuel cells will require an exterior shell or can. Seen here is the aluminum shell for our Class 11 rig. Aero Tech does not manufacture the outer sheet-metal shells but can refer customers to a reliable local shop for this service. The company has the ability to work from a blueprint, or customers can ship a fuel cell for custom construction.

Once the form is completed, and the fuel bladder readied for lamination, it is sprayed with a form-release agent to ensure that all the form materials are easily removed from the bladder once it's finished.

The first step in building a fuel bladder is to construct a paper mold or form. This form is slightly smaller than the outer shell to allow for the fuel bladder after lamination. Here, the mold for DIRTsports' Class 11 fuel cell is the example

The first two layers of the lamination are created with an .030-inch nitrile rubber fuel-barrier. The edges and corners overlap for increased strength and improved sealing.

With the two plies of nitrile fuel-barrier in place, an overlay of fuel-barrier adhesive and a protective layer of .045-inch rubber-coated nylon is applied. The result can be as thick as .250 inches at the corners and seams. This outer rubber layer offers better resistance to moisture than urethane. In order to eliminate air pockets and ensure a complete bond in the autoclave, every seam and corner must be rolled over. The locations for the fittings are marked per the customers' drawings and instructions.

Left: Before baking the fuel bladder, an ozone-resistant coating and the stencil block must be applied.

Right: The fuel bladder is baked in an autoclave for 4 hours at approximately 280 degrees F at a pressure of 80 psi. This results in a "welded" fuel cell: all layers are bonded under pressure and heat into one single,, continuous skin, yielding a much more reliable bladder than one with electronic welded seams or urethane lamination.

Once cooled, the bladder is soaked in water to soften the paper form. When the form is soft enough, it's simply removed by hand.

The fittings are installed in the fuel bladder, and then it's ready for fluid testing to check for leaks.

Now certified leak-free, the safety foam must be cut to fit the interior, so the fuel bladder won't collapse in the shell. The foam acts as an anti-slosh baffle for the fuel and, in the event of a puncture, reduces the spill area.

Above are samples of safety foam, two types of rubber lamination materials and just a few of the several fittings available from Aero Tech.

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The basics of a fuel cell consist of the outer shell or can, the safety foam for the inside, the fittings and--of course--the fuel bladder.